I bought a K&N replacement for mine. It "sliped on" just like the stock of course. I didn't see any performance improvement and I heard that the k/n with no outerwear does less of a job on dusty trails that the foam. So I returned it and got a new complete stock filter. It fits real tight for now which is all I wanted. I wondering if you put some water proof grease on the foam edge where it buts up wouldn't give it a little better seal. They way it is you feel like pulling over and checking your filter all the time. Unbelievable crappy design....

 

the very first performance mod according to 4wa for the warrior is that you get rid of the stock air filter set up. get a flow flange and put on a K&N or UNI filter.